About 252 million years ago, at the boundary between the Permian and Triassic periods, the vast majority of marine and terrestrial life died out in the most devastating extinction event in Earth’s history. Earth’s ecosystems eventually recovered, but not in the way — or as quickly as — scientists thought. In a new study looking at how marine species reemerged in the Triassic, researchers report a surprising trend of recovery from the top of the food chain down.

Mercury concentration spikes in the geologic record have been linked to massive volcanism in the form of large igneous provinces (LIP) such as the Deccan Traps, a kilometers-thick heap of basalt layers that formed in what is now India beginning late in the Cretaceous, and the Siberian Traps, an even larger mass of lava that erupted in Siberia at the end of the Per­mian. It’s thought that vast gas emissions associated with LIP eruptions could have significantly changed climate patterns and affected conditions such as ocean acidity.

About 252 million years ago, massive volcanic eruptions in what is now Siberia rapidly warmed Earth, resulting in the end-Permian mass extinction that saw most terrestrial and marine species die off. It’s been thought that surviving reptiles and fish fled the hot tropics and didn’t return for millions of years. But according to new research, the tropical evacuation may not have lasted so long after all.

During the Ordovician, between about 488 million and 444 million years ago, plant life first emerged on land, while primitive fish and a variety of marine invertebrates flourished in the oceans. Toward the end of the period, however, a mass extinction — the first of the so-called “Big Five” Phanerozoic extinctions — wiped out roughly 60 percent of all marine invertebrate genera. In a recent study, researchers shed new light on a possible cause of the Late Ordovician extinction: volcanic activity.

The end-Triassic mass extinction exterminated up to three-quarters of all species on land and in the oceans 201 million years ago. This die-off opened up ecological niches and allowed for, among other changes, dinosaurs to diversify and spread across terrestrial ecosystems during the rest of the Mesozoic. Volcanism has long been implicated in the extinction, but whether it had a major impact on the planet at the time has remained unclear. In new research, scientists observed elevated mercury concentrations in extinction-aged rocks from around the world. Because volcanism is the main nonanthropogenic source of mercury in the environment, the findings suggest that volcanic activity was likely the main extinction trigger at the end of the Triassic.

The end-Permian extinction event was disastrous for a wide range of organisms on land and in the sea, with as many as 70 percent of terrestrial and 81 percent of marine species dying off. One of the hardest hit marine phyla was the echinoderms, which today includes sea urchins and starfish. Echinoderms are thought to have suffered one of the most severe population reductions in evolutionary history, with only a few members surviving to repopulate the oceans in the Triassic. But in a new study, researchers have identified Triassic fossils from a handful of “hangover” species whose ancestors were previously thought to have gone extinct at the end of the Permian, suggesting the extinction wasn’t quite as cataclysmic for echinoderms as paleontologists have suspected.

The end-Permian extinction, nicknamed the “Great Dying,” is thought to be the deadliest mass extinction in Earth’s history. Many textbooks claim that up to 96 percent of marine life died out during this event, but a new study suggests this cataclysmic number has been overestimated.

After Earth’s most severe mass extinction, life took up to 9 million years to recover — millions of years longer than after other extinction events. New research published in Geology suggests that a collapse in the ocean’s productivity might have been the cause.